The present invention relates to a lens body tube configured to carry out a zooming operation and/or a focusing operation with a plurality of lenses being translated along the optical axis direction of the lens body tube using a cam ring.
In a lens body tube that is configured to carry out a zooming operation and/or a focusing operation with lenses incorporated in the lens body tube being translated along the optical axis direction of the lens body tube, a cam ring to be rotated is formed with cams, each of which is engaged with a corresponding one of cam followers provided at the side of the lenses. That is, accompanied by the cam ring being rotated integrally with a zoom ring or a focus ring being rotated during a zooming operation or a focusing operation, the lenses are translated along the optical axis direction of the lens body tube according to the shapes of the cams, with which the lenses are engaged, to carry out the zooming operation or the focusing operation.
A cam ring for simultaneously moving a plurality of lenses is required to be formed with a plurality of cams corresponding to the respective lenses. Recently, this kind of cam ring is fabricated by resin molding, and is generally formed in a metal mold that is divided in the optical axis direction. Therefore, when a plurality of cams are formed as cams protruded from the inner circumferential surface of the cam ring, and are arranged in the optical axis direction, it is hard to demold the cam ring from the metal mold because the plurality of cams lie in the way of the metal mold being released. For this reason, Japanese Unexamined Patent Publication No. HEI6-160688 discloses a technique where any adjacent two of cams in the circumferential direction is formed not to overlap in a releasing direction of a metal mold (in the optical axis direction). In addition, Japanese Unexamined Patent Publication No. 2003-202483 proposes a technique where one of a pair of cams is formed into a protruded shape, and the other is formed into a recessed shape.
For example, in the technique of Japanese Unexamined Patent Publication No. 2003-202483, as shown in FIG. 6, on the inner circumferential surface of a cam ring 2A that is fitted around the outer circumferential surface of an inner tube 11 of a main tube 1 of a lens body tube, there are formed a recessed cam 21A and a protruded cam 22A. The cams 21A and 22A are engaged with cam followers 32A and 42A that are included by lens groups 3 and 4 movable along a guide groove 112 extending in the optical axis direction in the inner tube 11, respectively. In this lens body tube, when the cam ring 2A is rotated, the cam followers 32A and 42A of the lens groups 3 and 4 are translated along the optical axis direction according to the shapes of the cams 21A and 22A, so that the lens body tube can be set in a desired zooming condition. Moreover, when the cam ring 2A is configured with the recessed cam 21A and the protruded cam 22A in this way, a metal mold for forming the cam ring 2A by resin molding is allowed to be configured as a pair of molds separated in the optical axis direction by the protruded cam 22A defined as a separating plane.
The technique disclosed in Japanese Unexamined Patent Publication No. HEI6-160688 cannot be applied to a lens body tube provided with two cams that are required to overlap in the optical direction. Especially, a recent lens body tube tends to be longer so as to accomplish a zooming operation with a greater change ratio of a focal length, and the technique is therefore hard to meet such a lens body tube. In addition, in any technique described in Japanese Unexamined Patent Publication No. HEI6-160688 and Japanese Unexamined Patent Publication No. 2003-202483, since each of a plurality of cams formed on the cam ring has an independent structure, each of the cams does not have a sufficient strength for bearing a stress that is applied from a cam follower provided at the side of a lens, and is thereby easy to be damaged. For this reason, the radial thickness of the cam ring is required to be more than a predetermined thickness, and is thereby an obstacle when the diameter of the cam ring is made smaller. Especially, in the technique of Japanese Unexamined Patent Publication No. 2003-202483 as shown in FIG. 6, at a portion, formed with the recessed cam 21A, of the cam ring 2A, it is necessary to make the radial thickness of the cam ring 2A thicker by a radial depth of the recessed cam 21A and to make the cam ring 2A protruded outward along the radial direction. Therefore, it is very difficult to make the diameter of the cam ring 2A smaller.